Visual C ++链接LNK2019错误与预编译的标头

I had a very weird problem with precompile header. The linker generates LNK2019: unresolved external symbol error when I implement method in .cpp file. However, the program could be compiled if I implement method in .h file. I happened to find out a solution but I have no idea about the root cause of this error.I had a very weird problem with precompile head